Doped carbon material coated sodium ferric pyrophosphate positive electrode material and preparation method thereof

Abstract

The invention relates to a preparation method of a doped carbon material coated sodium ferric pyrophosphate positive electrode material, which comprises the following steps: S1, mixing a sodium source, an iron source, a phosphorus source, a carbon source and a dispersing agent which are respectively weighed according to a stoichiometric ratio to obtain a premix; wherein the molar ratio of sodium to iron to phosphorus in the sodium source, the iron source and the phosphorus source is 4: 3: 4; adding water of which the mass is 3-5 times that of the premix into the premix, and stirring and dispersing to obtain dispersion liquid; s2, transferring the dispersion liquid into a sand mill, and sanding until the granularity of solid particles is 0.1-0.8 mu m, so as to obtain slurry; and S3, carrying out spray drying on the slurry, and sintering powder generated by spray drying in an inert atmosphere furnace to obtain the doped carbon material coated ferric sodium pyrophosphate positive electrode material. The dispersing agent is introduced into the sanding slurry, so that the sanding efficiency can be improved, and the dispersity and uniformity of the material can be improved; and meanwhile, a boron-containing dispersing agent and a nitrogen-containing carbon source are used for realizing co-doping on a product carbon layer, so that the electrochemical performance of the material is improved. The invention can effectively improve the discharge capacity and cycle life of the sodium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion battery materials, and particularly relates to a sodium iron pyrophosphate cathode material coated with a doped carbon material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have become the preferred solution for power batteries due to their high energy density and excellent performance. However, the scarcity and high price of lithium resources have restricted their development in the energy storage field. Sodium-ion batteries are expected to replace lithium-ion batteries in the energy storage field due to their low cost and rich resources. Among the cathode materials of sodium-ion batteries, polyanion materials have received extensive attention due to their low cost and good cycle performance. However, their poor conductivity restricts further commercial development.

[0003] Sodium iron pyrophosphate is a polyanion material that can be used as a cathode material for sodium-ion batteries. In the prior art, in order to improve the conductivity of sodium iron pyrophosphate, carbon materials are used for modification. The sand grinding spray drying process is simple in operation, low in cost, suitable for mass production, and the prepared material has good sphericity, and is also commonly used for the preparation of cathode materials. For example, CN116799131A discloses a preparation method of a porous sodium iron pyrophosphate / carbon composite material, including: weighing a sodium source, ferrous oxalate, a phosphorus source, and a carbon source according to a stoichiometric ratio, adding water, and dispersing evenly by a ball mill to obtain a dispersion; placing the dispersion in a sand mill and wet sand grinding for a certain time to obtain a slurry, the sand grinding time is 1-12 h, and the particle size of the sand ground slurry is controlled between 0.1-1 μm. Drying the water of the sand ground slurry by a spray dryer; sintering the powder after spray drying to obtain a porous carbon-coated sodium iron pyrophosphate / carbon composite material. The sodium source is one or more of sodium acetate, sodium carbonate, sodium citrate, and sodium chloride; the carbon source is one or more of soluble starch, glucose, polyethylene glycol, maltose, and cyclodextrin. Among them, ferrous oxalate is used as an iron source and a pore-forming aid, and a large number of small molecules generated by the decomposition of ferrous oxalate during high-temperature sintering overflow to form porous sodium iron pyrophosphate. The porous structure material prepared by this scheme improves the sodium ion transport efficiency and enables the battery material to have good rate performance.

[0004] In the above process, a sanding process is adopted. The purpose is to effectively reduce the particle size of the material, reduce particle agglomeration, and increase the specific surface area of the material. However, the sanding process often leads to a phenomenon where the smaller the particle size of the material, the more serious the agglomeration situation, especially during long-term sanding treatment. This not only reduces production efficiency but also further exacerbates the agglomeration problem among fine particles (which can be seen from its SEM image). Moreover, no dispersant component is used in this solution, making it even more impossible to solve the problem of agglomeration of small-particle materials. In addition, this solution only uses carbon materials to coat sodium iron pyrophosphate phosphate, and the effect of optimizing the conductivity of the material with an ordinary carbon layer is limited, and an improved solution needs to be further proposed. Summary of the Invention

[0005] (I) Technical problems to be solved

[0006] In view of the above-mentioned disadvantages and deficiencies of the prior art, the present invention provides a sodium iron pyrophosphate phosphate cathode material coated with a doped carbon material and a preparation method thereof. On the one hand, by introducing a dispersant, the sanding efficiency can be improved, and the dispersion and uniformity of the material can be enhanced. On the other hand, doping elements are introduced into the carbon material to improve the conductivity of the material. The present invention can further effectively improve the discharge capacity and cycle life of sodium batteries.

[0007] (II) Technical solutions

[0008] In the first aspect, the present invention provides a preparation method of a sodium iron pyrophosphate phosphate cathode material coated with a doped carbon material, which includes:

[0009] S1. Mix the sodium source, iron source, phosphorus source, carbon source, and dispersant weighed according to the stoichiometric ratio to obtain a premix; wherein, the molar ratio of sodium, iron, and phosphorus in the sodium source, iron source, and phosphorus source is 4:3:4; add 3 - 5 times the mass of water to the premix and stir to disperse it to obtain a dispersion;

[0010] S2. Transfer the dispersion to a sand mill and sand it until the particle size of the solid particles is 0.1 - 0.8 μm to obtain a slurry;

[0011] S3. Spray-dry the slurry, and sinter the powder generated by spray-drying in an inert atmosphere furnace to obtain a sodium iron pyrophosphate phosphate (Na4Fe3(PO4)2P2O7) cathode material coated with a doped carbon material.

[0012] According to a preferred embodiment of the present invention, in S1, the dispersant is at least one of polyethylene oxide, boric acid, and sodium tetraborate. PEO can rapidly dissolve in cold water to form a high-viscosity solution, which helps to uniformly disperse particles in the slurry, preventing sedimentation and agglomeration. The long-chain molecules of PEO physically adsorb on the particle surface to form a steric barrier, preventing direct contact between particles and thus inhibiting agglomeration. This property is particularly important in the preparation of high-solid-content slurries. As a non-ionic polymer, PEO avoids electrostatic interactions with charged particles, reducing particle aggregation caused by charge attraction.

[0013] According to a preferred embodiment of the present invention, in S1, the dispersant comprises polyethylene oxide and boric acid or the dispersant comprises polyethylene oxide and sodium tetraborate; or the dispersant further comprises a third dispersant in addition to the foregoing components, and the third dispersant is at least one of sodium hexametaphosphate, polyethylene glycol, ethylene oxide, propylene oxide, polyacrylamide, polypropylene ether, and polystyrene. When the dispersant contains sodium hexametaphosphate, sodium hexametaphosphate can decompose to form sodium oxide after sintering in an inert atmosphere and can be used as a sodium supplement agent.

[0014] According to a preferred embodiment of the present invention, in S1, the addition amount of the carbon source is determined according to the mass of the carbon material in the final product accounting for 0.8 - 4% of the mass of the product.

[0015] According to a preferred embodiment of the present invention, in S1, the addition amount of the dispersant accounts for 5 - 20% of the total mass of the carbon source.

[0016] According to a preferred embodiment of the present invention, in S1, the sodium source is at least one of sodium acetate, sodium citrate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium pyrophosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium sulfate, sodium sulfite, sodium hydroxide, and sodium benzoate; the iron source is at least one of ferrous sulfate, ferric sulfate, iron phosphate, ferrous oxalate, ferrous acetate, ferrous oxide, iron oxide, and magnetite; the phosphorus source is at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, phosphoric acid, iron phosphate, ammonium triphosphate, pyrophosphoric acid, and sodium pyrophosphate.

[0017] According to a preferred embodiment of the present invention, in S1, the carbon source is at least one of sucrose, glucose, polyacrylic acid, acetic acid, lactic acid, citric acid, starch, cellulose, asphalt, phenolic resin, polyimide, melamine, and polyaniline.

[0018] Preferably, the carbon source contains at least one of polyimide, melamine, and polyaniline, and may further contain other carbon sources, such as at least one of sucrose, glucose, polyacrylic acid, acetic acid, lactic acid, citric acid, starch, cellulose, asphalt, and phenolic resin.

[0019] Since polyimide, melamine, and polyaniline contain nitrogen elements, the amorphous carbon obtained after sintering in an inert atmosphere furnace contains nitrogen doping, which increases the concentration of hole carriers in the carbon layer and improves the conductivity of the product. When the dispersant contains boric acid or sodium tetraborate, a boron-nitrogen doped carbon material can also be formed after sintering, further improving the conductivity of the product.

[0020] It should be noted that when the dispersant is selected as boric acid and the carbon source is polyimide, the conductivity of the product is optimal when the mass ratio of the two is controlled at 1:4. This is mainly because when the boron doping in the carbon material is too low, the concentration of hole carriers in the carbon layer cannot be effectively increased, and when the doped boron element is excessive, too many holes neutralize the electrons provided by the nitrogen element, resulting in a decrease in conductivity. When boron and nitrogen are co-doped in an appropriate ratio, the two doping elements act synergistically, which can greatly improve the conductivity of the carbon layer and the product.

[0021] According to a preferred embodiment of the present invention, in S2, the sanding speed is controlled at 2000 - 3000 rpm, and the sanding time is 0.5 - 2 h.

[0022] According to a preferred embodiment of the present invention, in S3, the inlet air temperature of spray drying is controlled at 200 ± 30 °C, and the outlet air temperature is controlled at 105 ± 10 °C.

[0023] According to a preferred embodiment of the present invention, in S3, the sintering temperature is 480 - 600 °C, the sintering duration is 8 - 20 h, and the sintering atmosphere is at least one of nitrogen, argon, and hydrogen-argon mixed gas.

[0024] In the second aspect, the present invention also provides a sodium iron pyrophosphate positive electrode material coated with a doped carbon material, which is prepared by using the preparation method of any one of the above embodiments.

[0025] (III) Beneficial effects

[0026] The technical effect of the solution of the present invention lies in:

[0027] (1) By adding a certain proportion of dispersant to the dispersion liquid and then performing sanding, the present invention can improve the sanding efficiency, the dispersion degree and uniformity of the material, reduce the particle agglomeration phenomenon generated after a long time of sanding while increasing the specific surface area of the particulate material, improve the production efficiency of sanding, and make the particle size of the material reach a smaller particle size in a shorter time (increase the proportion of small-particle-size materials in the sanding slurry), which is beneficial to improving the electrochemical performance of the positive electrode material. When sintered in an inert atmosphere furnace, the dispersant and the carbon source decompose to generate gas overflow, making the product form a porous structure; thereby, the contact area between the positive electrode material and the electrolyte can be increased, the path of sodium ion deintercalation can be shortened, the ion diffusion speed can be increased, and the sodium battery has good electrochemical performance.

[0028] (2) In a preferred embodiment of the present invention, the dispersant used comprises a combination of polyethylene oxide and boric acid or a combination of polyethylene oxide and sodium tetraborate. The network structure of polyethylene oxide can significantly reduce the agglomeration of particles during sanding, improving the sanding rate and effect. At the same time, polyethylene oxide can also serve as a carbon source supplement. After sintering boric acid or sodium tetraborate, polyethylene oxide, and the carbon source in an inert atmosphere furnace, a boron-doped carbon material coating layer can be formed, which helps to increase the carrier concentration and the electrical conductivity of the material. Among them, when the selected carbon source is at least one of the nitrogen elements in polyimide, melamine, and polyaniline, a boron and nitrogen co-doped carbon material can be formed after sintering in an inert atmosphere furnace, further improving the electrical conductivity of the carbon material and the electrochemical performance of the product as a cathode material for sodium-ion batteries.

[0029] In addition, the sodium source and the dispersant boric acid can form sodium tetraborate, which has lubricity, can improve the fluidity of the slurry, is beneficial to the subsequent spray drying process, and can produce spherical powders with a uniform particle size distribution after drying.

[0030] (3) Under the same test conditions, compared with the sodium iron pyrophosphate / carbon composite material prepared by the prior art, the initial cycle capacity of the sodium iron pyrophosphate cathode material coated with a doped carbon material prepared in the preferred embodiment of the present invention is 1.1 - 1.2 times that of the prior art, and the charge-discharge efficiency is higher. In addition, the material prepared by the present invention has better long-cycle performance and can be used as a cathode material for sodium-ion batteries to prepare sodium batteries with a long service life.

[0031] In summary, the sodium-ion cathode material prepared by the present invention has a higher specific capacity and a longer cycle life, and the preparation process is simple, pollution-free, and the material has excellent performance, making it suitable for large-scale production applications. Description of the Drawings

[0032] Figure 1 SEM image of sodium iron pyrophosphate@doped carbon material prepared in Example 1 at Scale Bar = 20μm.

[0033] Figure 2 SEM image of sodium iron pyrophosphate@doped carbon material prepared in Example 1 at Scale Bar = 2μm. Detailed Embodiments

[0034] To better explain the present invention for easy understanding, the following provides a detailed description of the present invention through specific embodiments.

[0035] Example 1

[0036] This example provides a method for preparing a sodium iron pyrophosphate cathode material coated with a doped carbon material, and the steps are as follows:

[0037] (1) Weigh 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, 56.33 g of glucose, 15.29 g of polyimide, 3.82 g of boric acid, and 10.50 g of polyethylene oxide. After mixing them, add 4000 mL of deionized water (the mass of water is 3.56 times the mass of the mixture), and stir for 10 min with a blender to disperse and obtain a dispersion. Among them, the molar ratio of sodium, iron, and phosphorus satisfies 4:3:4. Glucose and polyimide are carbon sources, boric acid and polyethylene oxide are dispersants, sodium carbonate is the sodium source, iron phosphate is the iron source and phosphorus source, and ammonium dihydrogen phosphate is the phosphorus source. The dispersant accounts for 6% of the mass of the carbon source. The mass ratio of polyimide to boric acid is 4:1.

[0038] (2) Transfer the dispersion to a sand mill and grind it at a speed of 2700 rpm for 1 h to obtain a slurry. Test the average particle size of the slurry to be 400 nm and discharge the material.

[0039] (3) Use a spray dryer for spray drying. Set the inlet air temperature to 220 °C and the outlet air temperature to 100 °C. Collect the powder after spray drying; place the powder in a nitrogen atmosphere furnace and sinter it at 550 °C for 12 h with a heating rate of 2 °C / min to obtain a sodium iron pyrophosphate cathode material coated with a doped carbon material. The carbon material content in the product is 4%, the nitrogen element content is 0.442%, and the boron element content is 0.077%. Figure 1-2 The SEM picture of the product is shown. It can be seen that the surface of the product has a flaky coating layer.

[0040] Example 2

[0041] This example provides a preparation method of a sodium iron pyrophosphate cathode material coated with a doped carbon material. The steps are as follows:

[0042] (1) Weigh 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, 56.33 g of glucose, 15.29 g of polyimide, 1.91 g of boric acid, and 12.41 g of polyethylene oxide. After mixing them, add 4000 mL of deionized water (the mass of water is 3.56 times the mass of the mixture), and stir for 10 min with a blender to disperse and obtain a dispersion. Among them, the molar ratio of sodium, iron, and phosphorus satisfies 4:3:4. Glucose and polyimide are carbon sources, boric acid and polyethylene oxide are dispersants, sodium carbonate is the sodium source, iron phosphate is the iron source and phosphorus source, and ammonium dihydrogen phosphate is the phosphorus source. The dispersant accounts for 6% of the mass of the carbon source.

[0043] (2) Transfer the dispersion to a sand mill and grind it at a speed of 2700 rpm for 1 h to obtain a slurry. Test the average particle size of the slurry to be 400 nm and discharge the material.

[0044] (3) Spray drying was carried out using a spray dryer, with the inlet air temperature set at 220 °C and the outlet air temperature set at 100 °C. The powder was collected after spray drying; the powder was sintered in a nitrogen atmosphere furnace at 550 °C for 12 h with a heating rate of 2 °C / min to obtain a sodium iron pyrophosphate cathode material coated with a doped carbon material. The carbon material content in the product was 4.1%, the nitrogen element content was 0.441%, and the boron element content was 0.039%.

[0045] Example 3

[0046] This example provides a method for preparing a sodium iron pyrophosphate cathode material coated with a doped carbon material, and the steps are as follows:

[0047] (1) Weigh 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, 56.33 g of glucose, 15.29 g of polyimide, 5.73 g of boric acid, and 8.59 g of polyethylene oxide. After mixing them, add 4000 mL of deionized water (the mass of water is 3.56 times the mass of the mixture), and stir with a stirrer for 10 min to disperse, obtaining a dispersion. Among them, the molar ratio of sodium, iron, and phosphorus satisfies 4:3:4. Glucose and polyimide are carbon sources, boric acid and polyethylene oxide are dispersants, sodium carbonate is the sodium source, iron phosphate is the iron source and phosphorus source, and ammonium dihydrogen phosphate is the phosphorus source. The dispersant accounts for 6% of the mass of the carbon source.

[0048] (2) Transfer the dispersion to a sand mill and grind it at a speed of 2700 rpm for 1 h to obtain a slurry. The average particle size of the slurry was measured to be 400 nm, and then the slurry was discharged.

[0049] (3) Spray drying was carried out using a spray dryer, with the inlet air temperature set at 220 °C and the outlet air temperature set at 100 °C. The powder was collected after spray drying; the powder was sintered in a nitrogen atmosphere furnace at 550 °C for 12 h with a heating rate of 2 °C / min to obtain a sodium iron pyrophosphate cathode material coated with a doped carbon material. The carbon material content in the product was 3.90%, the nitrogen element content was 0.443%, and the boron element content was 0.116%.

[0050] Example 4

[0051] This example is the same as Example 1, except that 3.82 g of boric acid is replaced with 5.89 g of borax (sodium tetraborate hydrate), and the carbon source is changed from 56.33 g of glucose to 50.79 g of starch. Other steps and conditions are the same as those in Example 1.

[0052] Example 5

[0053] This example is the same as Example 1, except that 15.29 g of polyimide is replaced with 5.73 g of melamine, and the carbon source is changed from 56.33 g of glucose to 53.9 g of sucrose. Other steps and conditions are the same as those in Example 1.

[0054] Example 6

[0055] This example is the same as Example 1, except that 15.29 g of polyimide is replaced with 25 g of polyaniline, and 1.05 g of sodium hexametaphosphate is also added to the dispersant. Other steps and conditions are the same as those in Example 1.

[0056] Comparative Example 1

[0057] This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material coated with a doped carbon material. Specifically, all dispersants such as "boric acid and polyethylene oxide" are removed in Example 1, and at the same time, the carbon source "polyimide" is replaced with "glucose", that is, 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, and 71.62 g of glucose are weighed respectively. Other steps and conditions are all referred to Example 1.

[0058] Comparative Example 2

[0059] This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material coated with a doped carbon material. Specifically, all dispersants such as "boric acid and polyethylene oxide" are removed in Example 1, that is, 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, 56.33 g of glucose, and 15.29 g of polyimide are weighed respectively. Other steps and conditions are all referred to Example 1.

[0060] Comparative Example 3

[0061] This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material coated with a doped carbon material. Specifically, all of the dispersant "polyethylene oxide" in Example 1 is replaced with an equal amount of "polyethylene glycol", that is, 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, 56.33 g of glucose, 15.29 g of polyimide, 3.82 g of boric acid, and 10.50 g of polyethylene glycol are weighed respectively. Other steps and conditions are all referred to Example 1.

[0062] Comparative Example 4

[0063] This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material coated with a doped carbon material. Specifically, in Example 1, the carbon source "polyimide" was removed, that is, 281.93 g of sodium carbonate, 601.77 g of iron phosphate, 152.99 g of ammonium dihydrogen phosphate, 56.33 g of glucose, 3.82 g of boric acid, and 10.50 g of polyethylene oxide were weighed respectively. Other steps and conditions refer to Example 1.

[0064] The products prepared in the above examples and comparative examples were made into sodium-ion battery cathode sheets, and the preparation method was as follows: Weigh the products prepared in each example and comparative example, polyvinylidene fluoride binder (PVDF), and acetylene black conductive agent (AB) according to a mass ratio of 7:2:1, and add an appropriate amount of 1-methyl-2-pyrrolidone (NMP) solution and zirconia beads, which play the roles of adjusting viscosity and assisting mixing respectively. Subsequently, a mixed slurry was formed by vibrating ball milling, vibrating 8 times, 3 minutes each time. After removing the zirconia beads, the mixed slurry was evenly coated on the aluminum foil using a coating tool and vacuumed overnight at 60 °C. After drying, it was cut into electrode discs with a diameter of 12 mm. Select the electrode discs with uniform coating, weigh the electrode discs, and then the mass of the active material can be calculated to make the electrode loading 3 mg / cm 2 ), and then placed in a glove box with a high-purity argon atmosphere for standby.

[0065] Using metallic sodium as the anode, NaCR2032 type coin cells were assembled respectively and charged and discharged at a rate of 0.1C at 2 - 4V. The test results are shown in the following table.

[0066]

[0067]

[0068] As can be seen from the above table: within the test voltage range of 2 - 4V, Example 1 has an initial discharge specific capacity of 115.6 mAh / g. After cycling 100 times at a current of 0.1C, it still has a discharge specific capacity of 115.5 mAh / g, and its initial efficiency is the highest, reaching 92.6%. In Example 2, the reduction in the addition of boric acid led to a slight decrease in capacity. However, in Example 3, the excessive addition of boron disrupted the synergistic effect of boron-nitrogen co-doping in the carbon layer, resulting in a decrease in the electrical conductivity of the carbon layer, and the capacity was only 109.7 mAh / g. The test results of Examples 4 - 6 are relatively close to those of Example 1. However, in Comparative Example 1, due to the lack of boric acid, polyethylene oxide, and nitrogen-containing carbon source, this situation had a greater impact on the electrochemical performance of the product, resulting in a significant decrease in the electrochemical performance indicators of the product in Comparative Example 1. In Comparative Example 2, the dispersant was missing, but the nitrogen-containing carbon source was retained. There was a small amount of nitrogen doping in the product carbon layer, but no dispersant was used in the sanding slurry, resulting in severe agglomeration between the fine particle materials after sanding and poor sanding effect, thus making the electrochemical performance of the product also poor. After the dispersant in Comparative Example 3 was replaced from "polyethylene oxide" to "polyethylene glycol", the electrochemical performance of the product showed a downward trend compared with Example 1. It can be seen that when using PEO as the dispersant, its improvement effect on the product performance is better than that of the common polyethylene glycol dispersant. In Comparative Example 4, a nitrogen-free carbon source was used, and it was impossible to form a boron-nitrogen co-doping effect in the product carbon layer. Although the test results of the electrochemical performance of its product were better than those in Comparative Example 1, compared with the examples of the present invention, the electrochemical performance of its product decreased significantly.

[0069] In summary, the preparation process of the present invention has an obvious impact on the test results of the electrochemical performance of the product after adding a specific dispersant during the sanding process. When using PEO as the dispersant for the sanding slurry, PEO can reduce particle agglomeration, improve the dispersion uniformity of the material, and thus can better enhance the electrochemical performance of the final material. Using a boron-containing dispersant and a nitrogen-containing carbon source for product preparation realizes the boron-nitrogen co-doping effect on the carbon layer of the product, which can further enhance the electrical conductivity of the material, thereby significantly improving both the battery capacity and the initial efficiency.

[0070] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements, or in the case where the technical features in the above embodiments do not conflict with each other, can be combined in the manner recorded in the embodiments, and these modifications, replacements or combinations do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a sodium iron pyrophosphate cathode material coated with a doped carbon material, characterized in that, It includes: S1. Mix the sodium source, iron source, phosphorus source, carbon source and dispersant weighed according to the stoichiometric ratio respectively to obtain a premix; wherein, the molar ratio of sodium, iron and phosphorus in the sodium source, iron source and phosphorus source is 4:3:4; add 3 - 5 times the mass of water to the premix and stir to disperse to obtain a dispersion; S2. Transfer the dispersion to a sand mill and sand mill until the particle size of the solid particles is 0.1 - 0.8 μm to obtain a slurry; S3. Spray-dry the slurry, and sinter the powder generated by spray-drying in an inert atmosphere furnace to obtain a sodium iron pyrophosphate cathode material coated with a doped carbon material.

2. The preparation method according to claim 1, characterized in that, In S1, the dispersant is at least one of polyethylene oxide, boric acid and sodium tetraborate.

3. The preparation method according to claim 1, characterized in that, In S1, the dispersant contains polyethylene oxide and boric acid or the dispersant contains polyethylene oxide and sodium tetraborate; Or the dispersant further contains a third dispersant other than the foregoing components, and the third dispersant is at least one of sodium hexametaphosphate, polyethylene glycol, ethylene oxide, propylene oxide, polyacrylamide, polypropylene ether and polystyrene.

4. The preparation method according to claim 1, characterized in that, In S1, the addition amount of the carbon source is determined according to the mass of the carbon material in the final product accounting for 0.8 - 4% of the product mass.

5. The preparation method according to claim 1, wherein, In S1, the addition amount of the dispersant accounts for 5 - 20% of the total mass of the carbon source.

6. The preparation method according to claim 1, characterized in that, In S1, the sodium source is at least one of sodium acetate, sodium citrate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium pyrophosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium sulfate, sodium sulfite, sodium hydroxide and sodium benzoate; the iron source is at least one of ferrous sulfate, ferric sulfate, iron phosphate, ferrous oxalate, ferrous acetate, ferrous oxide, iron oxide and magnetite; the phosphorus source is at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, phosphoric acid, iron phosphate, ammonium phosphate, pyrophosphoric acid and sodium pyrophosphate.

7. The preparation method according to claim 2 or 3, characterized in that, In S1, the carbon source contains at least one of polyimide, melamine and polyaniline.

8. The preparation method according to claim 1, wherein In S2, control the sand milling speed at 2000 - 3000 rpm and the sand milling time at 0.5 - 2 h.

9. The preparation method according to claim 1, wherein, In S3, control the inlet air temperature of spray drying at 200 ± 30 °C and the outlet air temperature at 105 ± 10 °C; In S3, the sintering temperature is 480 - 600 °C, the sintering duration is 8 - 20 h, and the sintering atmosphere is at least one of nitrogen, argon and hydrogen - argon mixture.

10. A sodium iron pyrophosphate cathode material coated with a doped carbon material, characterized in that, It is prepared by the preparation method described in any one of claims 1 - 9.

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